#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;

main () {
  int num;
  double total;
  double inc;

  num = 0;
  total = 0;
  while ( cin >> inc ) {
    num++;
    total += inc;
  } 

  printf("%.6lf\n", total / num);
}
